In the last twenty years microprocessor speed increased by several orders of magnitude and Digital Signal Processors (DSPs) became ubiquitous. It became feasible and attractive to transition from analog communication to digital communication. Digital communication offers the major advantage of being able to more efficiently utilize bandwidth and allows for error correcting techniques to be used. Thus by using digital technology one can send more information through a given allocated spectrum space and send the information more reliably. Digital communication can use radio links (wireless) or physical network media (e.g., fiber optics, copper networks).
Digital communication can be used for different types of communication such as speech, audio, image, video or telemetry for example. A digital communication system includes a sending device and a receiving device. In a system capable of two-way communication each device has both sending and receiving circuits. In a digital sending or receiving device there are multiple staged processes through which the signal and resultant data is passed between the stage at which the signal is received at an input (e.g., microphone, camera, sensor) and the stage at which a digitized version of the signal is used to modulate a carrier wave and transmitted. After (1) the signal is received at the input and then digitized, (2) some initial noise filtering may be applied, followed by (3) source encoding and (4) finally channel encoding. At a receive device, the process works in reverse order; channel decoding, source recovery, and then conversion to analog. The present invention as will be described in the succeeding pages can be considered to fall primarily in the source encoding stage.
The main goal of source encoding is to reduce the bit rate while maintaining perceived quality to the extent possible. Different standards have been developed for different types of media.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.